1. Field of the Invention
This invention pertains to differentials and more particularly relates to a floating pinion pin type differential.
2. Description of Prior Art
A differential of the type having floating pinion pins is disclosed in U.S. Pat. No. to Pfarrwaller 3,779,102. The patentee discloses a differential having one bevel gear secured to a tubular shaft and the other bevel gear secured to a second shaft journaled within the tubular shaft. The pinions mesh with the bevel gears and are mounted on a yoke having the second shaft extending through an opening in the yoke. The pinions are journaled on threaded studs of the yoke and are held from axial movement relative to the studs by thrust bearings and nuts screwed onto the studs. The outer ends of the studs are provided with flats that are shorter than the diameter of the studs and are slidably received in slots formed in the inner periphery of a ring gear.
The United States Patent to Randall U.S. Pat. No. 3,342,084 does not disclose a floating pinion pin in a differential but instead discloses pinions with elongated or oversized bores which permit the pinions to float relative to the pinion pin and bevel gears thereby compensating for inaccuracies in machining tolerances or the like. The pinion pin is secured to the casing and does not float.
United States Pat. No. 1,445,864 to Alden discloses a differential with a plurality of pinions journaled on spindles of a spider. Flats are formed in the ends of the spindles and ride in slots in the ring gear or carrier so that rotation of the carrier will also rotate the spider. The thrust of Alden's pinions is absorbed by the carrier. It will be noted that the flats formed on the ends of the spindles are shorter than the diameter of the spindles.
In addition to the above patented differentials, applicants' assignee has manufactured a differential for several years which is substantially the same as the subject differential except that the pinion pin was a one-piece cylindrical pin having flats milled in the ends thereof for slidably engaging diametrically opposed slots in the carrier. The length of the flats, however, was shorter than the diameter of the pin, and the flats were not resiliently urged into the slots to assure maximum bearing contact between the flats and the sides of the slots regardless of tolerance stack-ups axially of the pinion pin.
Applicants have determined that premature differential failure has occurred with assignees' prior art differential mentioned above due to failure of the one-piece prior art floating pivot pin with flats that were shorter than the diameter of the pin. The reason for failure of the prior art pin is that the bearing area between the flats on the pin and the sides of the slots were inadequate. Applicants' first recognized that each reversal of one bevel gear relative to the other caused the pinions to rotate about the pinion pin. Even though the pinions rotated in opposite directions, this pinion rotation tended to also rotate the pinion pin, which rotation is prevented by the flats on the pinion pin engaging the sides of the slots. Each reversal of the direction of movement of the pinion pin caused diagonally opposite edges of the short flats of the prior art pin to be subjected to substantial amounts of rotation resisting force including impact forces. These impact loads on the flats, which occurred each time the bevel gears would rotate relative to each other, tended to hammer or forge the edges of the flats into circular configurations.
The rounding of the flats by this forging action is also accelerated by frictional wear between the edges and the sides of the slots when the pin ends slide back and forth in the slots due to variances in the gearing. This sliding action of the free floating pinion pin is due to the fact that the teeth of the two bevel gears do not rotate in truly parallel planes because of slight errors in machining, wear between the relative rotating parts, and other inaccuracies in the gearing.
Another reason for pin wear is that the ends of the one-piece prior art pins are not always fully seated in their slots and thus full bearing contact does not always occur between the flats and the sides of the slots. In this regard batches of pins and batches of carriers are made within prescribed tolerances. When a short pin is assembled in a carrier having the longest permitted distance between the bottom of the slots, it will be apparent that the ends of the one-piece pin can move axially of the pin in the slots thus causing frictional wear and also providing less than maximum bearing surface contact between the flats and the sides of the slots.